Magnetic recording medium, the manufacturing method and magnetic recording apparatus using the same

ABSTRACT

This magnetic recording medium is characterized in that in the magnetic recording medium having a magnetic film on a non-magnetic substrate by intercalating at least an under layer, the proportion of functional groups per 100 carbon atoms in a diamond-like carbon protective coating mainly composed of carbon for protecting the magnetic film exceeds 20%. The bonding force between the protective coating layer and the lubricating layer of the magnetic recording medium is increased so that under high speed rotation, a decrease in the lubricating layer is not caused so as to provide a magnetic recording apparatus having high reliability.

This is a division of application Ser. No. 09/784,952 filed 16 Feb.2001, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to a magnetic recording medium which hasexcellent reliability and in which magnetic recording is performed withhigh density, a manufacturing method thereof and a magnetic disc deviceused in an auxiliary storage apparatus of a computer.

A magnetic disc apparatus used in a storage apparatus of a large-scalecomputer, a work station, a personal computer and the like has beenyearly increased in its importance and developed into a mass-stored andsmall sized device. Increasing of recording density is essential to thedevelopment of the magnetic disc apparatus into mass-stored andsmall-sized apparatus. As the technology for realizing the developmentinto the mass-stored and small-sized device, cited is reduction indistance between a magnetic recording layer of a magnetic recordingmedium and a magnetic head.

The magnetic recording medium manufactured by sputtering has beenprovided with a protective coating heretofore for the purpose ofprotecting a magnetic film from sliding of a magnetic head. Thinning ofthe protective coating and reduction of distance between the surface ofthe protective coating and the magnetic head are the most effectivemeans for more decreasing the distance between a magnetic recordinglayer and the magnetic head. For this protective coating, carbonmanufactured by DC sputtering, RF sputtering (Japanese Patent Laid OpenHei 5-174369), or CVD (Japanese Patent Laid-Open No. Hei 4-90125) ismost generally used, and a method of mixing nitrogen atoms, hydrogenatoms and the like in the film to obtain a protective coating moreexcellent in strength (Japanese Patent Laid-Open No. Sho 62-246129) hasbeen generally adopted. Further, it is general to use perfluoropolyetherliquid lubricant for the purpose of reducing friction between themagnetic head and the magnetic recording medium.

As a general method for thinning, cited is to apply diamond-like carbon(DLC) using ion beam deposition (IBD) or chemical vapor deposition (CVD)for a protective coating. DLC, however, bonding strength of carbon atomsand hydrogen atoms in the thin film is generally strong and also itsnetwork has higher continuity as compared with the carbon protectivecoating provided by the sputtering. Therefore, the problem is that thebonding strength to perfluoropolyether lubricant applied to theprotective coating is weak owing to fewer functional groups.

One of performance indexes of the magnetic recording device using themagnetic recording medium is the data transfer rate. The data transferrate largely depends on the data access time. The access time iscomposed of the seek time and the rotation waiting time, and to shortenthe rotation waiting time by increasing the rotating speed of a magneticrecording medium leads to the improvement in the data transfer rate.

When the rotating speed of the magnetic recording medium is increased,however, centrifugal force is applied to the liquid lubricant on the DLCprotective coating of the magnetic recording medium so that as theresult of the problem that the bonding strength is weak, the liquidlubricant is driven away toward the outer peripheral part of themagnetic recording medium until it is shaken off from the magneticrecording medium (hereinafter referred to as spin-off). Consequently,the problem encountered is that the lubricant on the magnetic recordingmedium is decreased to increase the frictional force between themagnetic recording medium and the magnetic head and cause a crash.

In order to solve the problems, attempts have been made to apply surfacetreatment to the protective coating so as to increase the bondingstrength. Japanese Patent Laid-Open No. Sho 62-150526 and JapanesePatent Laid-Open No. Sho 63-2117 disclose that the surface is subjectedto plasma treatment. Japanese Patent Laid-Open No. Hei 4-6624 disclosesthat the surface is subjected to ultraviolet treatment, water treatment,ozonization or the like. Further, Japanese Patent Laid-Open No. Sho63-2117, Japanese Patent Laid-Open No. Hei 9-30596, Japanese PatentLaid-Open No. Hei 8-225791, Japanese Patent Laid-Open No. Hei 7-210850and Japanese Patent Laid-Open No. Hei 5-174354 are similar to the above,and all of these disclose that after the protective layer is formed, thesurface thereof is subjected to some treatment. These methods, however,have the problem that it is difficult to uniformly treat the wholesurface, one additional process is needed in the work, and besides theadhesion of the lubricant is insufficient.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstancesand provides a magnetic recording medium which is increased in thechemical bonding strength of a protective coating layer and liquidlubricant not to cause a decrease in liquid lubricant due to spin-offunder high speed rotation.

Further, the invention provides a manufacturing method for the abovemagnetic recording medium.

Further, the invention provides a magnetic storage apparatus suitablefor reconciling high speed rotation and high reliability by using theabove magnetic recording medium.

To solve the above problems, the invention mainly adopts the followingconstitution.

According to the invention, a magnetic recording medium is characterizedin that the magnetic recording medium has a magnetic film formed on anon-magnetic substrate by intercalating at least an under layer, and theproportion of functional groups per 100 carbon atoms in the diamond-likecarbon protective coating mainly composed of carbon, which protects themagnetic film, exceeds 20%.

In the case where a lubricating film of perfluoropolyether having atleast one functional group is provided on the protective coating,bonding performance between the protective coating and the lubricatingfilm is excellent.

According to the invention, a manufacturing method for the magneticrecording medium is characterized in that in the manufacturing methodfor the magnetic recording medium having a magnetic film formed on anon-magnetic substrate by intercalating at least an under layer, when aprotective coating mainly composed of carbon for protecting the magneticfilm is formed by an ion beam method or a chemical vapor depositionmethod, at least one gas among CO₂, NO₂, N₂O is added.

In the case where the protective coating is diamond-like carbon, thebonding performance between the protective coating and the lubricatingfilm is especially improved.

In the case of forming the protective coating by the ion beam method orthe chemical vapor deposition method, it is preferable to use at leastone of N₂, Ne, Ar, Kr and Xe and hydrocarbon gas or hydrocarbon gas.

In the manufacturing method for the magnetic recording medium having amagnetic film formed on a non-magnetic substrate by intercalating atleast an under layer, at the time of forming a diamond-like carbonprotective coating mainly composed of carbon for protecting the magneticfilm by an ion beam method or a chemical vapor deposition method, onegas among CO₂, NO₂, N₂O may be added.

According to the invention, a magnetic storage device is characterizedthat the device includes the magnetic recording medium, a driving partfor driving the magnetic recording medium, a magnetic head having arecording part and a reproducing part, a recording reproducing signalprocessing part for giving and receiving a signal to and from themagnetic head, and a magnetoresistive head as a reproducing part of themagnetic head.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will be described indetail based on the followings, wherein

FIG. 1 is a typical sectional view of a magnetic recording mediumaccording to the embodiment of the invention;

FIG. 2 is a schematic diagram of a protective coating forming chamber21;

FIG. 3 is a diagram showing the comparison of performance between themagnetic recording media provided according to the embodiment and thecomparative example of the invention;

FIG. 4 is a diagram showing the general construction of a magneticstorage device;

FIG. 5 is a typical perspective view of a magnetic head;

FIG. 6 is a diagram showing the sectional structure of amagnetoresistive sensor; and

FIG. 7 is a sectional view of a sensor using a spin valve head.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, the function, constitution and operation of the invention will bedescribed in brief in the following. In the manufacturing method for themagnetic recording medium having a magnetic film, a protective coatingmainly composed of carbon for protecting the magnetic film and alubricating film of perfluoropolyether having at least one functionalgroup provided on a substrate, at the time of forming the protectivecoating by an ion beam method using at least one of N₂, Ne, Ar, Kr, Xeand hydrocarbon gas, or only the hydrocarbon gas or a CVD method, thebonding performance between the protective coating and the lubricatingfilm is improved by adding at least one gas among CO₂, NO₂, N₂O.

In the magnetic recording medium provided by the above method, theproportion of functional groups per 100 carbon atoms in the protectivecoating can be over 20%.

The magnetic storage apparatus of the invention includes the magneticrecording medium, a driving part for driving the magnetic recordingmedium, a magnetic head formed by a recording part and a reproducingpart, a unit for moving the magnetic head relatively to the magneticrecording medium, a signal input unit for inputting a signal to themagnetic head and a recording reproducing signal processing unit forreproducing an output signal from the magnetic head, wherein thereproducing part of the magnetic head is formed by a magnetoresistivehead, and the magnetic recording medium is formed by the magneticrecording medium including the protective coating having the abovecharacteristic quality, hardness and thickness.

Further, the magnetoresistive sensor part of the magnetoresistive headis formed between two shield layers which are spaced from each other ata distance of 0.2 μm or less and made of soft magnetic substance, andthe product Br×t of the thickness (t) of the magnetic layer of the thusconstructed magnetic recording medium and the residual flux density Brmeasured by applying a magnetic field in the relative travelingdirection of the magnetic head to the magnetic recording medium inrecording ranges from 3.2 mA (40 gauss micron) to 9.6 mA (120 gaussmicron) both inclusive.

The reason why the magnetoresistive sensor part of the magnetoresistivehead is to be formed between two shield layers which are spaced fromeach other at a distance of 0.2 μm or less and made of soft magneticsubstance is that in the magnetic storage apparatus having the maximumtrack recording density of 220 kFCI, sufficient reproducing outputcannot be obtained. The distance between two shield layers made of softmagnetic substance is preferably 0.12 μm or more in view of workingeasiness.

The reason why the product Br×t of the thickness (t) of the magneticlayer of the thus constructed magnetic recording medium and the residualflux density Br measured by applying a magnetic field in the relativetraveling direction of the magnetic head to the magnetic recordingmedium in recording ranges from 3.2 mA (40 gauss micron) to 9.6 mA (120gauss micron) both inclusive is that when the Br×t is 3.2 mA (40 gaussmicron), the risk of reproducing wrong information becomes higher due tolowering of reproducing output caused by being left for long time afterrecording, and when it exceeds 9.6 mA (120 gauss micron), it becomesdifficult to overwrite in recording.

Further, by forming at least two layers of under layers in the magneticrecording medium, the crystal orientation of the magnetic layer may becontrolled. By forming such multiple under layer, the influence ofatomic diffusion from the under layer to the magnetic layer can beremarkably reduced, and simultaneously the crystallinity of the underlayer close to the magnetic layer can be improved, and the adhesionbetween the magnetic layer and the under layer becomes strong so as toobtain high sliding resisting performance. Further, since the surface ofthe under layer close to the magnetic layer has no atomic periodic arrayextending over a long distance, the crystal grains of the magnetic layerformed thereon may be refined and also the crystal orientation may becontrolled. Thus, the mean particle diameter of crystal constituting themagnetic layer is controlled to 15 nm or less suitable for reduction ofnoise, very fine size, and simultaneously the direction of the axis ofeasy magnetization may be controlled to be parallel to the film surfacesuitable for in-plane magnetic recording.

The magnetoresistive head used in the magnetic storage apparatus of theinvention is formed by a magnetoresistive sensor including pluralconductive magnetic layers causing a large resistance change due to arelative change of mutual magnetizing directions by an external magneticfield, and a conductive non-magnetic layer disposed between theconductive magnetic layers. The reason why the thus constructedreproducing head is used is that a signal recorded at the maximum trackrecording density exceeding 300 kFCI is stably reproduced to obtainsignal output.

Further, the magnetoresistive head is formed on a magnetic head slider,in which the area of the floating surface rail is equal to or smallerthan 1.00 mm² and the mass is equal to or less than 2 mg to achieve theinvention. The reason why the area of the floating surface rail is equalto or smaller than 1.00 mm² is that the probability of colliding withthe projection is reduced, and simultaneously, the shock resistancereliability can be improved by setting the mass equal to or less than 2mg. Thus, the recording density of 50 giga-bit per 1 in² and high shockresistance may be consistent with each other.

The embodiments of the invention will now be described in detail. FIG. 1shows one embodiment of the invention.

<Embodiment 1>

First, a soda lime glass substrate 1 (outside diameter of 84 mm, insidediameter of 25 mm and thickness of 1.1 mm) to be used is sufficientlywashed. This substrate is introduced into a vacuum vessel evacuated toabout 5.3×10E (−5)Pa (4.0×10E (−7)Torr). First, it is transported to afirst seed layer forming chamber to form a first seed layer 2 of Ni-25at. % Cr-15 at. % Zr with a thickness of 20 nm under the condition of Aratmosphere about 0.8 Pa (6 mTorr) by the DC magnetron sputtering method.Subsequently, it is transported to a second seed layer forming chamberto form a second seed layer 3 of Co-40 at. % Cr-5 at. % Zr with athickness of 50 nm under the condition of Ar atmosphere about 0.8 Pa (6mTorr) by the DC magnetron sputtering method. Subsequently, it istransported to a heating chamber in the vacuum layer to heat thesubstrate to the substrate temperature 260° C. by an infrared heater.

Subsequently, it is transported to an under layer forming chamber toform an alloy under layer 4 of Cr-10 at. % Mo-7.5 at. % Ti with athickness of 30 nm under the condition of Ar atmosphere about 0.8 Pa (6mTorr) by the DC magnetron sputtering method. Subsequently, it istransported to a magnetic recording layer forming chamber to form analloy layer 5 (to form a magnetic layer) of Co-20 at. % Cr-4 at. % Ta-8at. % Pt with a thickness of 22 nm under the condition of Ar atmosphereabout 0.9 Pa (7 mTorr) by DC magnetron sputtering method. By using thesubstrate where the alloy under layer 4 of Cr-10 at. % Mo-7.5 at. % Tiand the alloy layer 5 of Co-20 at. % Cr-4 at. % Ta-8 at. % Pt areformed, the protective coating layer which is mentioned later and mainlycomposed of carbon according to the invention is formed.

As the substrate 1, in addition to the soda lime glass, used is anon-magnetic rigid substrate formed of chemical reinforcedaluminosilicate, an Al—Mg alloy electroless-plated with Ni—P, silicon,ceramics made of borosilicate glass or the like, or ceramics subjectedto glass glazing or the like.

As the first and second seed layers are provided for avoidingelectrochemical precipitation of alkali metal from the soda lime glass,they may have an arbitrary thickness, and one layer will do. Further, ifnot needed, it may be omitted. The under layer 4 is used as a under filmfor controlling the crystal orientation of a magnetic layer formedthereon. As the under layer, used is a thin film of a Cr-group alloysuch as non-magnetic Cr—V, Cr—Ti, Cr—Mo, Cr—Si, Cr—Mo—Ti alloy formingan irregular solid solution which has good crystal consistency with themagnetic film and may be (100) orientated. When simultaneously 0.5 vol.% to 50 vol. % nitrogen is added to the gas for discharge used insputtering to form the under layer, the crystal grains of the underlayer are refined. As a result, the crystal grains of the continuouslyformed magnetic layer are also refined so that medium noise can bereduced.

As the magnetic layer 5, not only Co—Cr—Pt—Ta alloy, but a multi-alloyfamily material in which Co is taken as principal component, Pt iscontained to increase the coercive force, and further Cr, Ta, SiO₂, Nband the like to reduce medium noise are added may be used. Especially,when Ta, Nb, V, and Ti are added, the melting point of a target islowered, and composition separation of the magnetic film containing Cris easy to progress. This is favorable.

In the Co-group alloy family material to which Pt, Ni or Mn is added,lowering of magnetic anisotropic energy is less than that in the case ofother additive elements, so it is practical. To be concrete, in additionto Co—Cr—Pt, used are alloys such as Co—Cr—Pt—Ta, Co—Cr—Pt—SiO₂,Co—Cr—Pt—Mn, Co—Cr—Nb—Pt, Co—Cr—V—Pt, Co—Cr—Ti—Pt, Co—Cr—Nb—Ta—Pt,Co—Pt—Ni—SiO₂ and the like.

Concerning the composition of a Co alloy layer occupying a ferromagneticportion, it is considered that the solid solution limit of Cr is 5 to 10at. %, and the solid solution limit of Ta is about 2 at. %, and a Coalloy magnetic layer is formed exceeding these solid solution limits,whereby the magnetic separation in the magnetic layer progresses toreduce medium noise. As a practical composition, for example, thefollowings are used:

-   Co-20 at. % Cr-4 at. % Ta-8 at. % Pt alloy;-   Co-22 at. % Cr-20 at. % Pt alloy;-   Co-15 at. % Cr-8 at. % Pt-20 mol. % SiO₂ alloy;-   Co-17 at. % Cr-12 at. % Pt-5 at. % Mn alloy;-   Co-17 at. % Cr-5 at. % Nb-10 at. % Pt alloy;-   Co-20 at. % Cr-5 at. % V-12 at. % Pt alloy;-   Co-20 at. % Cr-10 at. %-15 at. % Pt alloy;-   Co-15 at. % Cr-5 at. % Nb-5 at. % Ta-20 at. % Pt alloy.

The above substrate is transported without being taken out from thevacuum vessel to a protective coating layer forming chamber 21 shown inFIG. 2. The protective coating forming chamber 21 is formed by an iongun including a heat filament 22, an anode 23 and a grid 24 disposed infront of the heat filament. While the protective coating forming chamber21 is evacuated by a turbo-molecular pump, from the rear of the anode,15 sccm (Standard Cubic centimeter per minutes) of Ar gas, 50 sccm ofethylene (C₂H₄) gas, further 20 sccm of carbon dioxide (CO₂) gas, 10sccm of nitrogen dioxide (NO₂) gas and 10 sccm of laughing gas (N₂O) areintroduced through a mass flow controller. At this time, the pressure isabout 0.5 Pa(4 mTorr) at the baratron gauge.

Subsequently, 30 A is applied to the heat filament of the ion gunspositioned on both sides of the substrate, DC+100V is applied to theanode to induce plasma, and then −530V is applied to the grid to deriveions. Further, pulse bias with −100V and 3 kHz is applied to thesubstrate. At this time, the anode current is 500 mA, and the biascurrent of the substrate is 50 mA. By this ion beam deposition method(IBD) , a DLC protective coating layer 6 mainly composed of carbon andhydrogen is formed 3 nm thick on the Co—Cr—Ta—Pt alloy layer 5. Thedeposition rate of coating at this time is 1.0 nm/s.

By the above method, plural discs are manufactured, some of them aresubjected to thin film analysis, and the other are provided with alubricant layer 7 of fluorocarbon family. The thickness of the layer is2.2 nm measured by quantitative analysis using Fourier-TransformInfraRed spectroscopic analyzer (FT-IR). After that, floating check isperformed to make a sliding test in a single plate, or the disc is builtin the magnetic disc apparatus to make a reliability test.

The protective coating of the disc manufactured by the above method isanalyzed by the following methods to measure the proportion offunctional groups of the protective coating surface. That is, ESCA(Electron Spectroscopy for Chemical Analysis) is used for identifyingthe covering rate of the functional groups of the protective coatingsurface. Direct identification of —COOH, —C═O, —COH, —CNH₂ which aresurface functional groups, using ESCA is difficult in view ofsensitivity and measurement accuracy. The above problems have beenovercome by the tag modification method described in the following.

That is, the covering rate identification is performed by modification(tag modification) using molecules which have functional groupsinteracting with the protective coating surface functional groupsquantitatively and irreversibly by molecular recognition, and containfluorine atoms which have high sensitivity coefficient to ESCA.

To be concrete,

-   -   To identify —COOH functional group, the protective coat surface        is dipped in a benzene solution of pentafluorophenyl bromide for        one hour to modify —COOH functional group with fluorine        molecules.    -   To identify —C═O functional group, the protective coating        surface is dipped in an ethanol solution of        pentafluorophenylhydrazine for one hour to modify —C═O        functional group with fluorine molecules.    -   To identify —COH functional group, the protective coating        surface is dipped in an ethanol solution of        perfluorooctyldimethylchlorosilane to modify —COH functional        group with fluorine molecules.    -   To identify —CNH₂ functional group, the protective coating        surface is dipped in a chloroform solution of        pentafluorobenzoylchloride for one hour to modify —CNH₂        functional group with fluorine molecules.

The respective protective coating surface tag-modified by one hourreaction at room temperature are dipped in the respective solvents toremove unreacted material from the protective coating surface.

In identifying the functional group covering rate of the protectivecoating surface, each tag-modified protective coating surface isobtained at an angle 24° of analysis of ESCA by Cls and Fls measurementintensity ratio, and as a result, the proportion of the functionalgroups —COOH, —C═O, —COH, —CNH₂ per 100 carbon atoms is about 30% on theaverage in total.

On the other hand, the disc provided with a lubricant is attached on anevaluating apparatus having a head load/unload mechanism to make a test.When load/unload test on ten discs are made 50000 times at a rotatingspeed of 15000 r.p.m, tests on all of ten discs are ended without crash.Further, when the thickness of the lubricating layer of the tested discis measured by FT-IR, it is confirmed that the thickness is hardlydecreased, 2.1 nm. As a result, it is proved that the magnetic recordingmedium of the invention has reinforced bonding force to the lubricant sothat a decrease in lubricant due to spin-off is small, and even in thecase where the thickness of the protective coating is very thin, 3 nm,sliding resisting reliability is sufficient. The above evaluation resultis described as sample No. 1 in FIG. 3.

COMPARATIVE EXAMPLE

Sample No. 2 is manufactured by the substantially same method as that ofthe embodiment 1 except that 10 sccm of carbon dioxide (CO₂) gas andnitrogen oxide (NO₂) gas and dinitrogen monoxide are not added at thetime of forming the protective coating layer 6. The thickness of theprotective coating layer 6 is 3 nm which is the same as that of theembodiment 1, and similarly the thickness of the lubricating layer 7 is2.2 nm. The thus manufactured disc is evaluated by the same method asthat of the embodiment 1.

As a result, in the tag modification analysis, the proportion of thesurface functional group is 13%. When load/unload test is made on tendiscs at the rotating speed of 15000 r.p.m, all of the discs cause crashduring the time from 1000 times to 8000 times. When the thickness of thelubricating layer is measured on ten discs by FT-IR, it is confirmedthat the thickness is decreased to 0.7 to 1.2 nm as compared with thatbefore the test.

As a result, it is known that in the magnetic recording medium obtainedby the manufacturing method of the comparative example, the bondingforce between the protective coating layer and the lubricating layer isnot enough so that the lubricating layer is scattered and decreased dueto high speed rotation, and the frictional force between the magneticrecording medium and the magnetic head is increased to cause crash.

<Embodiment 2>

When 5,0000 times load/unload tests are executed on the disc describedin the embodiment 1, in all of the magnetic recording medium taking thethickness of the magnetic film to be 15 nm, 17 nm and 21 nm, themagnetic recording media and the magnetic head are not broken down, sofavorable sliding resistance reliability is obtained.

By decreasing the thickness of the magnetic layer, the product Br×t ofthe thickness (t) of the magnetic layer and the residual magnetic fluxdensity Br is largely decreased. The in-plane coercive force Hcapproximately ranges from 176 kA/m to 256 kA/m, the coercivitysquareness S* is from 0.74 to 0.65, about 0.7, and the remanencesquareness is 0.78 to 0.7 (the remanence squareness S is the ratio ofthe residual flux density to the saturated flux density). These magneticcharacteristics are measured at 25° C. by a sample vibration typemagnetometer.

The electromagnetic transducing characteristics of these magneticrecording medium are measured by using a magnetic head constructed sothat the shield gap length Gs of the magnetoresistive reproducingelement (MR element) is 0.12 μm and the gap length of the write elementis 0.2 μm. The sense current of the MR element is set to 3 mA, and thewrite current I is set to 41 mA. The floating height of the head isvaried by changing the rotating seed of the magnetic recording medium(magnetic disc medium) to measure the output half width PW 50 of asolitary reproduced wave by a digital oscilloscope (Tektronix TDS 544).

The thinner the magnetic film is, and the lower the floating height ofthe magnetic head is, the smaller the PW 50 is. In the case where thethickness of the magnetic film is 15 nm and the floating height of thehead is 25 nm, a small value, 240 nm is obtained. The output at themaximum track recording density of 360 kFCI measured by the spectralanalyzer is 1 to 2% of the output of a solitary reproduced wave at 10kFCI measured by the digital oscilloscope. The output at the maximumtrack recording density of 360 kFCI measured by the spectral analyzer isintegrated and obtained until it exceeds the output of waveform of theodd order by 100 MHz.

Further, the ratio SLF/Nd of the integrated medium noise (Nd) in thecase where 0-p output (SLF) of the solitary reproduced wave and a signalof 360 kFCI are recorded is evaluated. The floating height of the headis taken as 25 nm, and Nd is taken as the integrated value of noise of aband corresponding to from 0.5 kFCI to 540 kFCI. In all of media, a highSLF/Nd ratio above 24 dB is obtained at the high recording density asmuch as 360 kFCI.

FIG. 4 shows the constitution of the magnetic storage apparatusincluding the magnetic disc medium 61, a driving part 62 for driving themagnetic recording medium, a magnetic head 63 formed by a recording partand a reproducing part, a unit 64 for moving the magnetic headrelatively to the magnetic recording medium, a signal input unit forinputting a signal to the magnetic head, a recording reproducing signalprocessing unit 65 for reproducing an output signal from the magnetichead, and a part 66 serving as a refuge place at the time of loading andunloading the magnetic head.

The reproducing part of the magnetic head is formed by amagnetoresistive head. FIG. 5 is a typical perspective view of themagnetic head used in measurement. The head is a composite head havingboth an electromagnetic induction type head for recording and amagnetoresistive head which are formed on a substrate 601. The recordinghead is formed by an upper recording magnetic pole 603 and a combinedlower recording magnetic pole and upper shield layer 604 which sandwichcoils 602, and the gap length between the recording magnetic poles is0.3 μm. For the coil, copper 3 μm thick is used. The reproducing head isformed by a magnetoresistive sensor 605 and electrode patterns 606 atboth ends thereof, the magnetoresistive sensor is sandwiched by thecombined lower recording magnetic pole and upper shield layer 604 and alower shield layer 607 which are 1 μm thick, and the distance betweenthe shield layers is 0.20 μm. In FIG. 6, the gap layer between therecording magnetic pole, and the gap layer 608 between the shield layerand the magnetoresistive sensor 608 are omitted.

FIG. 6 shows the structure of the section of the magnetoresistivesensor. The signal detection area 701 of the magnetic sensor is formedby a portion where a lateral bias layer 702, a separation layer 703 anda magnetoresistive ferromagnetic layer 704 are sequentially formed on agap layer 700 of aluminum oxide. Ni—Fe alloy 20 nm thick is used in themagnetoresistive ferromagnetic layer 704. Though Ni—Fe—Nb alloy 25 nmthick is used in the lateral bias layer 702, any ferromagnetic alloysuch as Ni—Fe—Rh and the like may be used if the electric resistance iscomparatively high and soft magnetic characteristic is favorable.

The lateral bias layer 702 is magnetized by a magnetic field formed by asense current flowing through the magnetoresistive ferromagnetic layer704 in the film in-plane direction (lateral direction) vertical to thecurrent, and lateral bias magnetic field is applied to themagnetoresistive ferromagnetic layer 704. Thus, selected is a magneticsensor showing the linear reproduction output to the leakage magneticfield from the medium 61. In the separation layer 703 for preventingeffective shunt current of sense current from the magnetoresistiveferromagnetic layer 704, Ta having comparatively high electricresistance is used, and the film thickness is taken as 5 nm.

Both ends of the signal detection area are provided with a taper part705 worked to be tapered. The taper part 705 is formed by a permanentmagnet layer 706 for making the magnetoresistive ferromagnetic layer 704into single magnetic domain, and a pair of electrodes 606 formed thereonfor taking a signal. It is necessary that the permanent magnet layer 706has large coercive force and the magnetizing direction is not easilychanged, and an alloy such as Co—Cr, Co—Cr—Pt or the like is used.

The magnetic storage apparatus shown in FIG. 4 is formed by combiningthe magnetic recording medium described in the embodiment 1 with thehead shown in FIG. 5. As a result, in the floating system in which themagnetic floating height hm is about 48 to 60 nm, when the product Br×tof the thickness (t) of the magnetic layer and the residual flux densityBr measured by applying a magnetic field in the relative runningdirection of the magnetic head to the magnetic recording medium inrecording exceeds 9.6 mA (120 gauss micron), satisfactory writing cannotbe performed, the overwrite characteristic is deteriorated, and theoutput especially in the high track recording density area is alsolowered.

On the other hand, when Br×t is smaller than 32 mA (40 gauss micron), insome case, it is found that being left at 70° C. for four days, thereproduction output is decreased in some composition or thickness of therecording layer of the medium. Accordingly, the magnetic storageapparatus is constructed so that the product Br×t of the thickness (t)of the magnetic layer and the residual magnetic flux density Br measuredby applying a magnetic field in the relative running direction of themagnetic head to the magnetic recording medium in recording mentioned inthe magnetic recording medium described in the embodiment 1 ranges from3.2 mA (40 gauss micron) to 9.6 mA (120 gauss micron) both inclusive.

In the case where the magnetoresistive sensor part of themagnetoresistive head uses a head formed between two shield layers whichare spaced from each other at a distance of 0.2 μm and made of softmagnetic substance, when the maximum track recording density exceeds 250kFCI, sufficient reproduction output cannot be obtained. When thedistance between two shield layers made of soft magnetic substance isbelow 0.12 μm, the element cannot be formed easily because of difficultyin process machining. Accordingly, the magnetic storage device is formedby using a head formed between two shield layers which are spaced fromeach other at a distance ranging from 0.12 μm to 0.2 μm both inclusiveand made of soft magnetic substance. By the thus constructed magneticstorage apparatus, the recording density equal to or higher than 50 gigabit per 1 in² can be realized.

<Embodiment 3>

A magnetic storage apparatus is formed by the same constitution as thatof FIG. 4 except that instead of the magnetoresistive head used in theembodiment 2, the magnetoresistive head 63 described in the embodiment 2uses a magnetic head formed by a magnetoresistive sensor includingplural conductive magnetic layers which cause a large resistance changedue to a relative change in mutual magnetizing directions by an externalmagnetic field and a conductive non-magnetic layer disposed between theconductive magnetic layers.

FIG. 7 shows the sectional view of the used sensor. The sensor has astructure in which a Ta buffer layer 801 5 nm thick, a first magneticlayer 802 with a thickness of 7 nm, an intermediate layer 803 made ofcopper 1.5 nm thick, a second magnetic layer 804 3 nm thick, and a Fe-50at. % Mn antiferromagnetic alloy layer 805 10 nm thick are sequentiallyformed on a gap layer 608. In the first magnetic layer 802, Ni-20 at. %Fe alloy is used, and in the second magnetic layer 804, cobalt is used.

By exchange magnetic field from the antiferromagnetic layer 805, themagnetization of the second magnetic layer 804 is fixed in onedirection. On the contrary, the direction of the first magnetic layer802 which is in contact with the second magnetic layer 804 byintercalating the non-magnetic layer 803 is varied by the leakagemagnetic field from the magnetic recording medium 61 so that theresistance change is caused.

Such resistance change caused by a change in the relative direction ofmagnetization of two magnetic layers is called spin valve effect. In thepresent embodiment, a spin valve head utilizing the effect for thereproducing head is used. The taper part 705 has the same constitutionas that of the magnetic sensor of the embodiment 2.

The Br×t of the magnetic recording medium used in measurement is takenas 3, 3.2, 4, 6, 8, 10, 12, and 14 mA. In the case where Br×t is takenas 3 mA (37.5 gauss micron), lowering of a reproducing signal causedwith the passage of time is extreme, and it is difficult to obtainpractically favorable coercive force. When Br×t exceeds 12 mA (150 gaussmicron), though the output of 2 F is large, the tendency of lowering theoutput resolution becomes remarkable so that it is not favorable.

When such a spin valve reproducing head is used, as described in theembodiment 2, a signal recorded at the maximum track recording densityexceeding 360 kFCI is stably reproduced to obtain signal output.

The head shown in here is the same as the head used in the embodiment 2,and the magnetoresistive head is formed on the magnetic head sliderconstructed so that the area of the floating surface rail is equal to orsmaller than 1.4 mm² and the mass is equal to or less than 2 mg. Settingthe area of the floating surface rail equal to or smaller than 1.4 mm²reduces the probability of colliding with the projection, andsimultaneously setting the mass equal to or less than 2 mg can improveshock resistance reliability. Thus, high recording density and highshock resistance can be reconciled, and the average failure timeinterval (MTBF) equal to or longer than 30,0000 hours at the recordingdensity equal to or higher than 50 giga bit per 1 in² can be realized.

According to the invention, the bonding performance between theprotective coating and the lubricating film can be reinforced.Furthermore, a mass-stored and high reliability magnetic disc apparatuscan be provided by combining the magnetic recording medium with themagnetic head.

1. A manufacturing method for a magnetic recording medium, the magneticrecording medium having a magnetic film on a non-magnetic substrateformed by intercalating at least an under layer, comprising forming aprotective film mainly composed of carbon for protecting the magneticfilm by an ion beam method or a chemical vapor deposition method, inwhich at least one gas among CO₂, NO₂, N₂O is added.
 2. Themanufacturing method for a magnetic recording medium according to claim1, wherein the protective coating is diamond-like carbon.
 3. Themanufacturing method for a magnetic recording medium according to claim1, wherein when the protective coating is formed by the ion beam methodor the chemical vapor deposition method, at least one of N₂, Ne, Ar, Kr,Xe and hydrocarbon gas or hydrocarbon gas is used.
 4. A manufacturingmethod for a magnetic recording medium, the magnetic recording mediumhaving a magnetic film on a non-magnetic substrate formed byintercalating at least an under layer, comprising forming a diamond-likecarbon protective coating mainly composed of carbon for protecting themagnetic film by an ion beam method or a chemical vapor depositionmethod, in which at least one gas among CO₂, NO₂, N₂O is added.
 5. Amanufacturing method for a magnetic recording medium, the magneticrecording medium having a magnetic film, a protective coating mainlycomposed of carbon for protecting the magnetic film and a lubricatingfilm of perfluoroether having at least one functional group on anon-magnetic substrate, comprising forming the protective coating by anion beam method or a chemical vapor deposition method using at least oneof N₂, Ne, Ar, Kr, Xe and hydrocarbon gas or hydrocarbon gas, in whichat least one gas among CO₂, NO₂, and N₂O is added.
 6. A manufacturingmethod of a magnetic recording medium comprising the steps of: formingan under layer on a non-magnetic substrate; forming a magnetic filmabove said under layer; forming a diamond-like carbon film above saidmagnetic film layer by a chemical vapor deposition method in which N₂Ogas is added.
 7. The manufacturing method of a magnetic recording mediumfurther comprising the steps of: forming a lubricating film ofperfluoroether on said diamond-like film.